1. Field of the Invention
The present invention relates to an automatic selecting apparatus for an optimum wireless communication route capable of automatically selecting an optimum communication route according to a purpose out of a plurality of wireless communication routes in a portable terminal which can utilize a plurality of wireless communication infrastructure (referred to merely as an infrastructure hereinafter) having different characteristics.
2. Description of the Background Art
In the field of wired communication using a public line, there is an LCR (Least Cost Routing) function as a known technique (Japanese Patent Laid-Open Publication Nos. HEI 1-180172, HEI 2-94754 and HEI 6-113042). The LCR function is the function of automatically selecting a line that can be used at the least cost when an operator estimates and inputs the place, day of the week time and line connection time of communication with the other party in using a telephone among the proposed carriers of DDI, Teleway Japan and Japan Telecom inclusive of the NTT line.
However, portable telephones and the like of wireless communication systems do not have the LCR function because each terminal can join only one cellular carrier.
Also, in the future, it is highly possible that not only the wireless line exchange system used in each cellular carrier but also the infrastructure of the wireless packet exchange system such as a tele-terminal will be popularized though the service area of the latter is narrow yet currently.
It is suspected that the portable terminals of wireless communication systems have several problems as follows.
First, in a portable terminal capable of using a plurality of infrastructures having different characteristics through wireless line exchange and wireless packet exchange that are expected to appear in future, it is presumably difficult for each user to decide which infrastructure should be used at an arbitrary point of time. It is considered that the optimum infrastructure may change depending on the purpose of use of each user, and therefore, the above difficulty further increases.
Secondly, in a data communication using a cable, it is often that the state of an electric signal is always constant and in good conditions between terminals which exchange communications. Therefore, it is scarcely required to consider the signal intensity, and the possible occurrence of data communication error depending on the signal intensity is ignorably little. In contrast to the above, in a data communication using a wireless route, the electric field intensity extremely varies to vary the communication error, and therefore, it is very difficult to estimate the communication error.
Thirdly, in regard to the LCR function in wired communication, the charge for communication is uniquely decided when the communication route, the destination party to be connected and the time of communication are decided. Therefore, it is relatively easy to select the communication route that costs the least expensive charge for communication. In contrast to the above, in the case of wireless communication, the distance from the base station to the wireless terminal and the communication conditions of the wireless communication route are not fixed. Therefore, the charge for communication is not uniquely decided even when the communication route, the destination party to be connected and the time of communication are decided.
Fourthly, in the case of data communication using a cable, there is relatively less data communication error. Therefore, assuming that a plurality of communication routes are used, it is considered that the shortness of the time of communication is approximately proportional to the magnitude of the transfer rate of the communication route. However, it is considered that the data communication error occurs frequently in the case of the data communication using a wireless route. Then, how to process the data communication error depends on the wireless communication system to be used, and for the above process are availed a system for retransmitting the portion in which an error has occurred and a system for additionally transmitting data necessary for error correction in the data communication stage and correcting the error at the receiving end when an error is detected. Therefore, in the case of the data communication using a wireless route, the shortness of the time of communication is not always proportional to the magnitude of the transfer rate in contrast to the case of the wired communication, and this means that the selection of the communication route for achieving the fastest data communication is difficult.